Conditional Cross Join - Why doesn't this work on the 'ON' clause?, PostgreSQL

Language: Layout:

CREATE TABLE user_tbl AS SELECT * FROM ( VALUES
 ('u9876',201504,201610)
,('u5564',201602,201612)
,('u4435',201606,NULL)
) AS t(user_id, start_yearmonth, end_yearmonth);

CREATE TABLE date_range AS SELECT * FROM ( VALUES
 (201601),(201602),(201603),(201604),(201605),(201606),(201607),(201608),(201609),(201610),(201611),(201612),(201701),(201702)
) AS t2(yearmonth);

-- Check user_tbl output
SELECT * FROM user_tbl ;

-- Check date_range output
SELECT * FROM date_range ;

-- SUCCESSFUL CROSS JOIN
SELECT
    *
FROM
    user_tbl
    CROSS JOIN date_range
WHERE
    user_tbl.start_yearmonth <= date_range.yearmonth     -- EXAMPLE: FOR u5564, 201601 IS NOT <= 201602, SO IT IS NOT RETURNED
    AND (user_tbl.end_yearmonth >= date_range.yearmonth  -- EXAMPLE: FOR u5564, 201701 IS NOT >= 201702, SO IT IS NOT RETURNED
         OR user_tbl.end_yearmonth IS NULL)              -- EXAMPLE: FOR u4435, NO ROWS RETURNED UNLESS NULL VALUES ARE ALLOWED TO BE CROSS JOINED
ORDER BY 
    user_tbl.user_id, date_range.yearmonth ;
    
    
    
-- UNSUCCESSFUL CROSS JOIN - WHY WON'T THIS WORK IN THE 'ON' CONDITION?
SELECT
    *
FROM
    user_tbl
    CROSS JOIN date_range ON user_tbl.start_yearmonth <= date_range.yearmonth     
                             AND (user_tbl.end_yearmonth >= date_range.yearmonth  
                                 OR user_tbl.end_yearmonth IS NULL)              
ORDER BY 
    user_tbl.user_id, date_range.yearmonth


Absolute service time: 0,5 sec, absolute service time: 0,51 sec